Combination continuous woven-fiber and discontinuous ceramic-fiber structure

ABSTRACT

A method of fabricating a ceramic structure as well as a pre-ceramic preimpregnated composite material incorporating a continuous woven fiber and a discontinuous fiber pre-ceramic matrix for subsequent curing and component construction. The method includes preparation of a mixture of discontinuous fibers, fillers, and a pre-ceramic precursor resin where the precursor resin is present in a quantity sufficient to substantially saturate subsequently adjacent woven fiber lengths, and thereafter introducing the mixture to a situs between an upper length of woven fiber and a lower length of woven fiber in alignment with each other while effectuating linear movement of these woven fiber lengths and moving the lengths toward each other for compression and retention in a sandwich configuration to thereby fabricate a pre-ceramic preimpregnated composite material. The material is cut to size in accord with the configuration of a part to be manufactured, formed into a green-state structure, and cured. Finished-product characteristics show a substantially uniform distribution of discontinuous fibers and fillers within the ceramic resin matrix to thereby provide a substantially internally stress-free end product component.

FIELD OF THE INVENTION

This invention is an application and division of 09/378,843 filed Aug.23, 1999 U.S. Pat. No. 6,222,313 and relates in general to a structureof woven fiber and discontinuous fiber immersed in a ceramic matrix, andin particular to the construction of such a structure having asandwich-configuration with an upper length of woven fiber and a lowerlength of woven fiber in alignment with each other and having disposedtherebetween a substantially uniform distribution of discontinuousfibers within a ceramic resin matrix optionally containing a fillermaterial.

BACKGROUND OF THE INVENTION

Employment of a ceramic based structure for the fabrication of certaincomponents that require the chemical and mechanical properties of suchconstruction is well recognized and non-limitedly exemplified in thinceramic armor. One such structure that could be beneficial is a curedsandwich configuration comprising an upper length of ceramic-resinimpregnated woven fiber and a lower length of ceramic-resin impregnatedwoven fiber in alignment with each other and having disposedtherebetween discontinuous fibers optionally including filler materialwithin a ceramic resin.

However, the present method of fabricating a combination of woven anddiscontinuous fibers unfortunately yields an inherently stressed endproduct that is not properly usable in many applications. Theintroduction of stress is caused by fabrication techniques which includelaying a number of ceramic precursor resin-wetted woven fabric plies ina mold, adding a quantity of a mixture of discontinuous fibers,precursor resin, and, as desired, filler powders to the mold, andcompressing the mold to form a green-state structure for subsequentceramic conversion of the matrix by pyrolysis. Because the exposedsurface of the fabric is uneven and erratic due to the weave at thebottom of the mold, the mixture containing the discontinuous fibers doesnot flow smoothly during compression of the mold, thereby resulting inboth a nonuniform distribution of the mixture and a clumping of mixtureat certain sites while causing degradation of mechanical properties of afinished part. Where clumping occurs, more pressure is placed on thewoven fabric to thereby enhance non-uniformity of fiber volume andthickness of the woven section so affected. Second, and again due tonon-uniformity of the mixture coupled with high molding pressures, asubstantial number of internal stress points are introduced within themixture in its green state. The stresses can cause warpage of thestructure during pyrolytic curing and thereby substantially reduceutility of the structure for component fabrication.

In view of the above prior art construction methodology and resultantend product, it is apparent that a need is present for methodology andconsequent end product wherein a continuous woven fiber and adiscontinuous ceramic fiber can be coupled in a ceramic matrix toproduce an end product having favorable properties for ceramicstructural applications. Accordingly, a primary object of the presentinvention is to provide methodology for fabricating a precursor ceramicpreimpregnated composite material comprising a continuous woven fiberand a discontinuous fiber combined with a ceramic precursor resin withor without filler powders for subsequent curing and non-stressedcomponent construction.

Another object of the present invention is to provide methodology forfabricating, as well as an end product of, a woven-fiber anddiscontinuous-fiber ceramic matrix composite structure for subsequentcomponent construction.

Yet another object of the present invention is to provide a curedwoven-fiber and discontinuous-fiber ceramic matrix composite structurehaving uniform distribution of discontinuous fibers within a ceramicresin.

These and other objects of the present invention will become apparentthroughout the description thereof which now follows.

SUMMARY OF THE INVENTION

The present invention is a method of fabricating a ceramic structure aswell as a precursor ceramic preimpregnated composite material comprisinga continuous woven fiber and a discontinuous fiber combined with aceramic precursor resin with or without a filler material for subsequentcuring and component construction. The method comprises preparation of amixture of discontinuous fibers with or without filler particles and aceramic precursor resin where the precursor resin is present in aquantity sufficient to substantially saturate subsequently adjacentwoven fiber lengths, and thereafter introducing the mixture to a situsbetween an upper length of single or multiple-ply woven fiber and alower length of single or multiple-ply woven fiber in alignment witheach other while effectuating linear movement of these woven fiberlengths and moving the lengths toward each other. The opposing upper andlower lengths of woven fiber, with the mixture of discontinuous fibers,with or without a filler material, and a ceramic precursor resintherebetween, are compressed and retained in a sandwich configuration tothereby substantially saturate the woven fiber with ceramic precursorresin and fabricate a preimpregnated composite material for subsequentcomponent fabrication.

The resultant preimpregnated composite material yields apart-fabrication material from which parts requiring ceramic propertiescan be manufactured. Such a material provides an upper length ofpre-ceramic resin impregnated woven fiber and a lower length ofpre-ceramic resin impregnated woven fiber in alignment with each otherwith a substantially uniform distribution therebetween of discontinuousfibers with or without filler material within a pre-ceramic resin. Thematerial is cut to size in accord with the configuration of the part tobe manufactured, and then is formed via conventional polymer compositeforming techniques non-limitedly exemplified by vacuum form, compressionmold, etc. to provide a green-state structure. The structure then iscured by pyrolysis in accord with conventional techniques to produce afinished-product whose characteristics show a substantially uniformdistribution of discontinuous fibers and filler material if presentwithin the ceramic matrix to thereby provide a substantially internallystress-free end product.

BRIEF DESCRIPTION OF THE DRAWINGS

An illustrative and presently preferred embodiment of the invention isshown in the accompanying drawings in which:

FIG. 1 is a schematic illustration of methodology for fabricating acontinuous woven fiber and a discontinuous fiber/filler ceramicprecursor resin for subsequent component construction; and

FIG. 2 is a flow diagram outlining methodology for the fabrication of acontinuous/discontinuous fiber ceramic matrix finished part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a schematic mixture-deposition system 10 is shownfor fabricating a precursor ceramic preimpregnated composite materialcomprising a continuous woven fiber. and a discontinuous fiber combinedwith a ceramic precursor resin with or without a filler material forsubsequent curing and component construction. In particular, twoopposing lengths of woven fiber, which can be single or multiple ply,are arranged to provide an upper length 14 and lower length 16 thereofin alignment with each other and each moving linearly in the directionof the arrow 18. Two opposingly disposed circular rollers 20, 22 arepositioned to bring the fiber lengths 14, 16 near each other while amixture 24 of discontinuous fibers, with or without fillers, and aceramic precursor resin is introduced for placement between the fiberlengths 14, 16.

The precursor ceramic resin of the mixture 24 is present in a quantitysufficient to substantially saturate the subsequently adjacent wovenfiber lengths 14, 16, and preferably, but not necessarily, is polymerderived while being most preferably, but not solely, chosen from thegroup consisting of BLACKGLAS (AlliedSignal Corporation [e.g. resin no.EMRC 493E]), CERASET (DuPont-Lanxide Corporation), SYLRAMIC (Dow-CorningCorporation), and STARFIRE (Starfire Corporation) resins. Thediscontinuous fibers of the mixture 24 preferably are of a cylindricalrice-like configuration of a length between about 0.125 inch to about0.25 inch. Most preferably, the woven material and discontinuous fibersare chosen from the group consisting of alumina, Nextel 312, Nextel 440,Nextel 510, Nextel 550, silicon nitride, silicon carbide, HPZ, graphite,carbon, peat, and mixtures thereof. Preferably, the fibers can be coatedwith an interface material non-limitedly taking the form of at least one0.1-0.5 micron-thick layer of at least one of carbon, silicon nitride,silicon carbide, silicon carboxide, and boron nitride. If desired,filler material can be included, and can nonlimitedly be chosen from thegroup consisting of alumina, mullite, titania, silicon carbide,graphite, silica, boron nitride, and boron carbide.

As shown in FIG. 1, the opposing woven fiber lengths 14, 16 are movedtoward each other while the mixture 24 is introduced between the lengths14, 16 for final compression and retention in a sandwich configurationby a conventional clamp compression device 26. As noted above, theprecursor resin of the mixture 24 is present in a quantity sufficient tosubstantially saturate the woven fiber lengths 14, 16, and such wettingoccurs upon compression and retention of the woven lengths 14, 16. Inthis manner, a precursor pre-ceramic preimpregnated composite material28 is produced comprising resin-saturated woven lengths 14, 16 havingdisposed therebetween the discontinuous fiber/filler resin mixture 24.

Referring to FIG. 2, methodology for production of a composite componentconstructed from the pre-ceramic preimpregnated composite material 28first includes cutting the material 28 in accord with the configurationof a particular component to be manufactured. This cut piece of materialis then formed into a green-state structure which can be accomplished byplacing the material into a conventional compression mold form. Thegreen-state structure thereafter is cured in accord with the curingcharacteristics of the precursor ceramic resin employed (e.g. pyrolysis)to thereby fabricate a woven-fiber and discontinuous-fiber ceramicmatrix composite component part. The component part so fabricated has agenerally uniform distribution of discontinuous fibers, as well asfiller material when included, within a matrix to thereby providereduced internal stress within the part. Such construction providesgreater utility and longevity to the part itself and resultantly, ofcourse, to the article of manufacture within which the part isincorporated.

While an illustrative and presently preferred embodiment of theinvention has been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

What is claimed is:
 1. A pre-ceramic preimpregnated composite materialof sandwich-configuration comprising an upper length of pre-ceramicresin impregnated woven fiber and a lower length of pre-ceramic resinimpregnated woven fiber in alignment with each other and having disposedtherebetween a substantially uniform distribution of discontinuousfibers within a pre-ceramic resin.
 2. A pre-ceramic preimpregnatedcomposite material as claimed in claim 1 wherein the discontinuousfibers are cylindrical of a length between about 0.125 inch to about0.25 inch.
 3. A pre-ceramic preimpregnated composite material as claimedin claim 1 wherein the fibers are chosen from the group consisting ofalumina, Nextel 312, Nextel 440, Nextel 510, Nextel 550, siliconnitride, silicon carbide, HPZ, graphite, carbon, peat, and mixturesthereof.
 4. A pre-ceramic preimpregnated composite material as claimedin claim 1 wherein the pre-ceramic resin is a polymer derived precursorresin.
 5. A pre-ceramic preimpregnated composite material as claimed inclaim 4 wherein the polymer-derived resin is chosen from the groupconsisting of BLACKGLAS, CERASET, SYLRAMIC, and STARFIRE resins.
 6. Apre-ceramic preimpregnated composite material as claimed in claim 1wherein the mixture additionally comprises a filler material.
 7. Apre-ceramic preimpregnated composite material as claimed in claim 6wherein the filler material is chosen from the group consisting ofalumina, mullite, titania, silicon carbide, graphite, silica, boronnitride, boron carbide, and mixtures thereof.
 8. A pre-ceramicpreimpregnated composite material as claimed in claim 1 wherein thefibers are coated.
 9. A method as claimed in claim 8 wherein the fibersare coated with a coating chosen from the group consisting of carbon,silicon nitride, silicon carbide, silicon carboxide, and boron nitride.